1.8 16v compression test confusion
OHOE
Hi, I did a compression test on my 16v today and all cylinders were between 215
and 220psi. The Chiltons (I don't have a Bentley yet) says it should be 148 to
189. Am I going crazy or is this just another example of how bad Chiltons
sucks?
TIA,
Oliver Hoen
Dave Latta
No, the Chilton book is correct. The 148-189 is for a new car, too...I believe the low limit is about 108-110 to compensate for wear. Maximum deviation between cylindars is something around 44. Check your equiptment.
OHOE <oh...@aol.com> wrote in article <19980926200537...@ng147.aol.com>...
Mk1_GTi
<bi...@badger5.demon.co.uk> wrote:
>I have similar figures for my 16v motor too. 230psi to 240psi and my equipment is calibrated to UK NAMAS standards.
>It does'nt sound like there's much wrong with your test results to me.
>
>regards
>Bill
> Dave Latta wrote in message <01bde9c1$01a9b120$1607ed81@buster>...
Carbon buildup in the combustion chamber ???
Matt
'80 MkI Golf GTi
'86 MkII Golf GTi
'90 Corrado G60 (For Sale)
'92 MkII Golf GTi 16V
Badger5
racer...@my-dejanews.com
bad90g@*nospam*epix.net (Mk1_GTi) wrote:
> On Mon, 28 Sep 1998 16:52:50 +0100, "Badger5"
> <bi...@badger5.demon.co.uk> wrote:
>
>
> Matt
>
> '80 MkI Golf GTi
> '86 MkII Golf GTi
> '90 Corrado G60 (For Sale)
> '92 MkII Golf GTi 16V
>
Maybe the head had been shaved at one time? Did you buy the car used or new?
--
Bob C 97 GTI VR6 DE
85 GOLF ITB
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OHOE
>Maybe the head had been shaved at one time? Did you buy the car used or new?
>--
I had thought about that, the car is used. But isn't the valve clearance to
close to shave enough off to make a difference of probably 50 psi or so? That's
more than 25% of the compression at new spec. But who knows?
Oliver
racer...@my-dejanews.com
Yes it would be close tolerances in there. Think about it, It's not really 50
lbs from the high end of the spec. Maybe a little inaccuracy in the
compression gauge also. Just make sure timing is no more than factory spec
and use 92-93 octant. Most people would have to pay a bunch of money to get
10.5 to one. Thats the range BTW that early Audis with 10.6 to one tested at.
thesc...@juno.com
oh...@aol.com (OHOE) wrote:
>
> >Maybe the head had been shaved at one time? Did you buy the car used or new?
> >--
>
> I had thought about that, the car is used. But isn't the valve clearance to
> close to shave enough off to make a difference of probably 50 psi or so?
That's
> more than 25% of the compression at new spec. But who knows?
> Oliver
How are you performing the compression test?
How long do you crank it?
How does the engines compression ratio, 10:1, effect the cylinders sealing
ability.
A new 8v JH engine has a compression between 131-174 psi.
A new 16v, PL or 9A, engine has a compression between 145-189 psi.
On my '88 16v, the compression is 175 psi and the '87 is 180 psi
in every cylinder.
The 16 valve engine has a higher compression ratio and a higher
cylinder compression.
But isn't that because of it having more valves per cylinder?
If the 16 valve engine had a compression ratio of 8.5:1, it would
probably still be higher than the 8v.
Peter
thesc...@juno.com
'88 Scirocco 16V
'87 Scirocco 16V
'87 GTI 16V
'83 GTI
'81 Pickup
'81 Scirocco S
OHOE
>How are you performing the compression test?
with a gauge and hose that screws into the spark plug hole.
>How long do you crank it?
about 5 seconds, sometimes a little longer. Until the pressure maxes out on the
gauge.
>How does the engines compression ratio, 10:1, effect the cylinders sealing
>ability.
Got me there:) No idea
>
>A new 8v JH engine has a compression between 131-174 psi.
>A new 16v, PL or 9A, engine has a compression between 145-189 psi.
>
>On my '88 16v, the compression is 175 psi and the '87 is 180 psi
>in every cylinder.
>The 16 valve engine has a higher compression ratio and a higher
>cylinder compression.
>But isn't that because of it having more valves per cylinder?
As far as I know the # of valves has nothing to do with CR. It's just volume at
BDC vs. volume at TDC.
>
>If the 16 valve engine had a compression ratio of 8.5:1, it would
>probably still be higher than the 8v.
>
>
Why? I don't understand this.
Thanks,
Oliver.
Christos Papadopoulos
Here is how I perform a compression test on my A1 Jetta.
See if you like it, or if there are any suggestions on how
to improve it.
1. Run engine until fully warmed up. Oil temp must be more
than 80C (if you have an oil temp gauge) or let the fan
cycle at least twice, Better still, take it for a short
ride on the highway.
2. Remove all spark plugs, set aside, remember where each goes.
Also remove the central HT wire from teh distributor and
ground it (important to avoid damage to the coil).
3. Remove the plastic duct from fuel distributor to throttle.
4. Attach compression tester to #1 cylinder.
5. Have assistant crank the engine while flooring the accelerator.
6. Try to read the initial reading if possible. Let the engine
crank until reading stabilizes. Write down reading.
7. Repeat for other cylinders.
Notes:
(i) Having the engine up to operating temp is important
to get true results. The same for flooring the accelerator.
(ii) Removing the duct to the throttle valve will keep the
plate in the airflow meter from rising and your injectors
from spraying. Another way to do this is to remove the
fuel pump relay, but I like having an unobstructed air
passage to the cylinders for this test (i.e., get the
plate out of the path). Of course, if you like, you can
do both!
Christos.